Automation Direct DL205 Manual page 33

Relay Output Six output modules in the DL205 I/O family feature relay outputs: D2–04TRS,
Guidelines D2–08TR, D2–12TR, D2–08CDR, F2–08TR and F2–08TRS. Relays are best for the
following applications:
Some applications in which NOT to use relays:
Relay outputs in the DL205 output
modules are available in two contact
arrangements, shown to the right. The
Form A type, or SPST (single pole, single
throw) type is normally open and is the
simplest to use. The Form C type, or
SPDT (single pole, double throw) type has
a center contact which moves and a
stationary contact on either side. This
provides a normally closed contact and a
normally open contact.
Some relay output module's relays share
common terminals, which connect to the
wiper contact in each relay of the bank.
Other relay modules have relays which
are completely isolated from each other. In
all cases, the module drives the relay coil
when the corresponding output point is on.
Surge Suppresion Inductive load devices (devices with a coil) generate transient voltages when
For Inductive de-energized with a relay contact. When a relay contact is closed it "bounces", which
energizes and de-energizes the coil until the "bouncing" stops. The transient
Loads
voltages generated are much larger in amplitude than the supply voltage, especially
with a DC supply voltage.
When switching a DC-supplied inductive load the full supply voltage is always
present when the relay contact opens (or "bounces"). When switching an
AC-supplied inductive load there is one chance in 60 (60 Hz) or 50 (50 Hz) that the
relay contact will open (or "bounce") when the AC sine wave is zero crossing. If the
voltage is not zero when the relay contact opens there is energy stored in the
inductor that is released when the voltage to the inductor is suddenly removed. This
release of energy is the cause of the transient voltages.
When inductive load devices (motors, motor starters, interposing relays, solenoids,
valves, etc.) are controlled with relay contacts, it is recommended that a surge
suppression device be connected directly across the coil of the field device. If the
inductive device has plug-type connectors, the suppression device can be installed
on the terminal block of the relay output.
•
Loads that require higher currents than the solid-state outputs can
deliver
•
Cost-sensitive applications
•
Some output channels need isolation from other outputs (such as when
some loads require different voltages than other loads)
•
Loads that require currents under 10 mA
S
Loads which must be switched at high speed or heavy duty cycle
I/O Wiring and Specifications
Relay with Form A contacts
Relay with Form C contacts
DL205 Installation and I/O Manual, Rev. B
3–9